As disclosed in U.S. Pat. Nos. 8,065,826 and 8,210,444 and as shown in FIG. 1 a typical assembly for securing a railroad rail 10 to an underlayment 11, typically of concrete, comprises a generally flat mounting plate 12 and clips 14 holding the rail 10 down on the plate 12. The rail 10 is secured to the plate 12 very solidly such that the rail 10 cannot move transversely in direction T of its running direction relative to the mounting plate 12. This plate 12 is typically secured in turn by several bolts 15, normally four, that have shanks threaded into anchors 16 set in the concrete 11 and heads bearing downward via at least one washer on the plate 12.
Since the exact placement of the anchors 16 in the concrete underlayment 11 can never be perfect, the plate 12 is normally formed with short transversely extending slots through which the bolts 15 extend, allowing the mounting plate 12 to be positioned transversely before the bolts 15 are torqued down to lock the plate 12 in place.
Because of the enormous transverse forces that are exerted, in particular in nonstraight regions of the rail 10 at, for example, a turnout, it is necessary to provide something more than a simple frictional engagement of the bolt 15 with the mounting plate 12 to prevent transverse shifting of the plate 12 on the substrate 11 when, for instance a heavy high-speed train is passing.
Hence it is standard in the art to form the plate 12 at each of the bolts 15 with an array of longitudinally extending and upwardly pointing ridges 17 that are transversely uniformly spaced at, for example, 5-10 mm. Similarly the bolt 15 is fitted with an adjuster plate 18 having a circular central hole of a diameter only slightly greater than a diameter of a shank of the bolt 15, and formed with downwardly directed and longitudinally extending ridges 18 complementary to the ridges 17 of the plate 12. With such an arrangement when the bolt 15 is torqued down atop the adjuster plate 18, the interengaging teeth 17 and 18 and snug bore lock the plate 12 to the bolt 15, thereby creating an interfitting coupling that works on shear, not simply on friction. This solidly locks the plate 12 against transverse displacement relative to the bolts 15 fixed in the substrate 11.
This system has the disadvantage that with a modern high-speed train it is important to perfectly transversely position the rails relative to each other. The existing system only allows a relatively coarse indexing, typically in steps of 3.125 mm, that does not allow the rails to be positioned with the accuracy required for trains moving at speeds that are a multiple of what was once considered possible.
The obvious solution to this process is to provide more closely spaced ridges, but this does not work as such ridges are inherently smaller and subject to being sheared off if loaded transversely beyond a load that might be encountered when a train rounds a curve or passes through a turnout moving at high speed.